1. Field of the Invention
The present invention relates to a cap type metallic sealing element, which is coupled to both ends of an anode-supported tubular solid oxide fuel cell having various sectional shapes, such as a cylindrical shape or a flat tubular shape, so as to easily and precisely seal the both ends of the anode-supported tubular solid oxide fuel cell such that the anode-supported tubular solid oxide fuel cell can efficiently collect electric charges, and a method for sealing both ends of an anode-supported tubular solid oxide fuel cell by coupling a cap type metallic sealing element to the both ends of the anode-supported tubular solid oxide fuel cell by means of brazing.
2. Description of the Prior Art
A fuel cell technology is a highly efficient clean power generation technology capable of directly converting hydrogen contained in hydrocarbon based materials, such as natural gas, coal gas or methanol, and oxygen contained in air into electric energy through an electrochemical reaction. Fuel cells are mainly classified into alkaline fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells and polymer fuel cells according to the type of electrolytes used for the fuel cells.
In general, the fuel cell uses hydrogen gas, which mainly consists of hydrogen and is obtained by reforming fossil fuel, and oxygen contained in air as fuel thereof. The phosphoric acid fuel cell (PAFC) using a phosphoric acid electrolyte is called a “first generation fuel cell”, the molten carbonate fuel cell (MCFC) using molten carbonate as an electrolyte thereof and operating at the high temperature of about 650° C. is called a “second generation fuel cell”, and the solid oxide fuel cell (SOFC) operating at the temperature higher than that of the MCFC and generating power with the highest efficiency is called a “third generation fuel cell”.
Although the SOFC called a “third generation fuel cell” has been developed after the PAFC and the MCFC, since the technology has rapidly advanced, the SOFC is expected to be used in practice very soon, together with the PAFC and the MCFC. To this end, many advanced countries concentrate efforts on the research and development of the SOFC technology.
The SOFC operates at the high temperature in a range of about 600 to 1000° C. In addition, the SOFC represents the highest efficiency from among various conventional fuel cells while minimizing environmental pollution. Also, the SOFC can realize combined power generation without requiring a fuel reformer.
The SOFC is classified into a tubular SOFC and a flat SOFC. A power density in a stack of the tubular SOFC is slightly lower than that of the flat SOFC, but a power density in a system of the tubular SOFC is similar to that of the flat SOFC. However, the tubular SOFC represents superior resistance against thermal stress and unit cells forming the stack of the tubular SOFC can be easily sealed. In addition, the stack of the tubular SOFC has a higher mechanical strength, so that the tubular SOFC can be fabricated in a large size. For this reason, studies and research have been actively performed with respect to the tubular SOFC. The tubular SOFC is again classified into a cathode-supported tubular SOFC using a cathode as a supporter for the fuel cell and an anode-supported tubular SOFC using an anode as a supporter for the fuel cell.
The anode-supported tubular SOFC is more advanced than the cathode-supported tubular SOFC, and studies and research for the tubular SOFC are focused on the anode-supported tubular SOFC.
The anode-supported tubular SOFC has a tubular structure having various sectional shapes, such as a cylindrical shape and a flat tubular shape. As shown in FIG. 1, the anode-supported tubular SOFC 1 or 1′ includes an anode 11 or 11′, an electrolyte layer 12 or 12′ and a cathode 13 or 13′, which are sequentially stacked from an inner portion of the anode-supported tubular SOFC 1 or 1′. For the purpose of electrical connection, a connection member 14 is provided on an outer peripheral portion of the anode 11 or 11′ such that the connection member 14 may protrude from the outer peripheral portion of the anode 11 or 11′ without making contact with the cathode 13 or 13′.
At this time, in the case of the anode-supported flat tubular SOFC 1′, since the width of the anode-supported flat tubular SOFC 1′ is relatively larger than the height of the anode-supported flat tubular SOFC 1′, a plurality of parallel bridges B servicing as supporters are vertically installed between an inner bottom portion and an inner top portion of the anode 11′ in order to reinforce the strength of the anode-supported flat tubular SOFC 1′.
In the anode-supported cylindrical SOFC 1 or the anode-supported flat tubular SOFC 1′ having the above structure, fuel gas must be fed through a hollow path formed in the anode 11 or 11′ while maintaining both ends of a unit cell in a sealed state. To this end, conventionally, a sealing element made of glass or glass ceramic is provided to both ends of the fuel cell so as to seal the both ends of the fuel cell from the exterior.
However, in the case of the anode-supported cylindrical SOFC 1 or the anode-supported flat tubular SOFC 1′ having the connection member 14, it is difficult to completely seal the both ends of the fuel cell because of a geometrical sectional shape of the connection member 14. In addition, a sealing portion is very weak against thermal impact.
In order to solve the problem derived from the geometrical sectional shape of the connection member 14, as shown in FIG. 2, a fuel cell 2 or 2′ including an anode 11 or 11′, an electrolyte layer 22 or 22′ and a cathode 23 or 23′ has been developed without the connection member 14. However, if the sealing element is coupled to the above fuel cell 2 or 2′, the anode cannot directly collect electric charges due to the insulation characteristic of the sealing element.
That is, the electric charges must be collected by means of a collection wire connected to the anode 11 or 11′ by passing through the sealing element from the exterior, so that the internal resistance of the fuel cell 2 or 2′ may increase, degrading the performance of the fuel cell 2 or 2′.